As a planarization technology in manufacturing of semiconductor devices, a chemical mechanical polishing technology is employed. The chemical mechanical polishing is a technique wherein an object to be polished is brought into contact with a polishing pad under pressure and the object to be polished and the polishing pad are slid on each other with feeding a chemical mechanical polishing dispersion onto the polishing pad to chemically and mechanically polish the object to be polished. The chemical mechanical polishing dispersion used herein generally contains various chemicals such as an etching agent and a complexing agent in addition to abrasives. After the polishing, therefore, abrasives and polishing dust sometimes remain on the polished surface. In the case where a wiring comprising a metallic material is present on the polished surface, metal ions chemically abstracted from the polishing surface by the action of the chemicals contained in the chemical mechanical polishing dispersion are readsorbed on the polished surface, and hence, contamination of the polished surface sometimes takes place inevitably.
With extremely high integration of semiconductor devices in recent years, contamination by impurities has exerted great influences on the performance of the semiconductor devices and in its turn on the yield of the manufactured articles, even if the impurities are in trace amounts. On this account, more strict contamination control than before has been required.
One of such contamination controls is cleaning on a polished surface after the polishing operation, and methods for removing contamination of a polished surface using various cleaning agents have been proposed.
For example, in order to remove contamination of an insulating film after chemical mechanical polishing, a cleaning method using a cleaning agent containing hydrofluoric acid or ammonia has been proposed (see “Hydrogen Peroxide Solutions for Silicon Wafer Cleaning”, RCA Engineer, 28(4), p. 9 (1983) and “Clean Solutions Based in Hydrogen Peroxide for Use in Silicon Semiconductor Technology”, RCA Review, 31, p. 187 (1970)). The cleaning agent containing hydrofluoric acid, however, corrodes metallic materials, so that this agent cannot be applied to semiconductor substrates having a metal wiring portion. The cleaning agent containing ammonia also corrodes metallic materials, particularly copper, so that this agent cannot be applied to semiconductor substrates having a copper wiring portion that is the main stream in recent years.
On the other hand, cleaning agents containing citric acid as a main ingredient have been proposed as cleaning agents which do not corrode metallic materials (see Japanese Patent Laid-Open Publication No. 72594/1998 and “Semiconductor World”, No. 3, p. 92 (1997)). However, it cannot be said that these cleaning agents have sufficiently high contamination-removing capability, and they cannot meet the requirements of the recent strict contamination control.
From the above viewpoints, there have been desired cleaning agents which exhibit sufficiently high contamination-removing capability and meet the requirements of the recent strict contamination control without corroding metallic materials, particularly copper.